The present invention relates generally to implantable leads and catheters and more particularly to mechanisms for deflecting implantable leads and catheters to assist in guiding them through the vascular system.
Over the years, quite a number of mechanisms have been disclosed and employed to deflect catheters and implantable leads. These have taken the form of deflectable guidewires and deflectable stylets, typically operable from the proximal end of the lead or catheter, which controllably impart a curve to the distal portion of the lead or catheter. One group of devices comprise deflectable stylets or guidewires which employ a straight, tubular outer member with a curved inner member, the inner and outer members movable relative to one another. Examples of this type of deflection mechanism are disclosed in U.S. Pat. No. 4,136,703 issued to Wittkampf and U.S. Pat. No. 5,728,148 issued to Bostrom et al. Alternatively, deflection devices employing a curved outer member and a relatively straight inner member are also known to the art, as disclosed in U.S. Pat. No. 4,676,249 issued to Arenas and U.S. Pat. No. 5,040,543 issued to Badera et al. In devices of both types, the relative position of the inner member with respect to the outer member determines the degree to which the curved member (inner or outer) is allowed to display its preset curvature.
A more commonly employed approach to providing controllable deflection employs a Generally straight outer member and a tension or push wire located within the outer member which on advancement or retraction causes the outer member to bend. Examples of such deflection mechanisms can be found in U.S. Pat. No. 4,815,478 issued to Buchbinder et al., and U.S. Pat. No. 4,940,062 issued to Hampton et al.
Particularly in the context of deflectable stylets intended for use in conjunction with implantable medical leads such as pacing and cardioversion leads, steerable stylets employing this third type of deflection mechanism are disclosed in U.S. Pat. No. 5,662,119 issued to Brennen et al., U.S. Pat. No. 5,170,787 issued to Lindegren and U.S. Pat. No. 5,327,906 issued to Fideler et al, all of which are incorporated herein by reference in their entireties.
While all of the mechanisms disclosed in the above cited prior art patents are at least to some degree workable, there is still a perceived need for a deflectable stylet or guidewire which has the capability to impart a controllable, relatively small radius curvature to the distal end of a cardiac pacing lead or catheter and which is sufficiently durable to allow for repeated use.
The present invention includes a variety of embodiments of deflectable stylets or guidewires all including an elongated tubular portion which may be fabricated of nitinol, stainless steel or other appropriate metal and which may take the form, for example, of a length of hypodermic tubing, preferably stainless steel, super-precision drawn, smooth-bore tubing. Located at the distal end of the tubing is a deflectable tip portion which in turn includes a coil, coupled to the distal tip of the tube; preferably fabricated of wire which is rectangular in cross-section and wound into a flat-wound coil such that the width of the wire is greater than the thickness of the wire measured radially. A longitudinally movable internal tension or push wire is located within the tube and extends through the coil to the distal end of the coil where it is mechanically coupled to the distal end of the coil. Also provided is a backbone member which may take one of several forms and which is configured to prevent longitudinal compression and/or expansion of the coil along one side thereof so that longitudinal movement of the wire within the tube and coil causes deflection of the coil. The coiled wire, tension/push wire and the backbone may be fabricated of stainless steel, nitinol, or other appropriate material. In particular, the coil and backbone are preferably formed of a wrought stainless steel, more preferably a precipitation hardened stainless steel such as PH 15-7 Mo or 17-7PH or similar alloys which, in their annealed condition are readily weldable and which may be shaped by precision stamping and coiling. The backbone member is also preferably configured to prevent out of plane twisting of the coil as a result of longitudinal movement of the internal wire, and more preferably is configured to provide a smooth and even bend by preventing relative movement of individual turns of the coil relative to one another, along one side of the coil.
In a first embodiment, the backbone takes the form of an elongated member provided with laterally extending projections which are sized to fit between adjacent turns of the coil along one side of the coil allowing compression or expansion of the coil only along the opposite side of the coil in response to longitudinal movement of the internal wire. The projections of the backbone also prevent relative longitudinal movement of individual turns of the coil along the side of the coil engaging the backbone, providing a smooth, continuous bend. The backbone is preferably coupled to the coil at its tip and may optionally be welded to the coil along its length, at some or all of the points at which the projections of the backbone contact individual turns of the coil. In this embodiment, the backbone preferably has a generally arcuate configuration in cross section, and has a width substantially greater than its arc height in order to provide a preferred bending axis and prevent out of plane twisting of the deflectable portion of the stylet or guidewire during longitudinal movement of the internal wire.
In a second embodiment, the backbone takes the form of a tube having external threads formed thereon which correspond to the spaces between the turns of the coil. In this embodiment, the tube is provided with a longitudinal slot or recess such that over a portion of the length of the tube, the tube engages the coil only along one side thereof, allowing compression or expansion of the coil only along the opposite side of the coil in response to longitudinal movement of the internal wire. In this embodiment, the backbone also has a generally arcuate configuration in cross section along the length of the slot, and along this length also has a width substantially greater than its arc height in order to provide a preferred bending axis and prevent out of plane twisting of the deflectable portion of the stylet or guidewire during longitudinal movement of the internal wire. The backbone is preferably coupled to the coil at its tip and may optionally be welded to the coil along its length, at the points at which the projections of the backbone contact individual turns of the coil.
A third embodiment of the invention employs a backbone taking the form of an elongated member having a generally arcuate configuration in cross section, but which does not include projections as set forth in conjunction with the first and second described embodiments. The backbone is instead welded to the coil at one or more locations between its proximal and distal end to prevent relative movement of the individual coils.
A final alternative embodiment to the present invention integrates the backbone with the coil itself. In this case, the coil is formed of a material such as the PH15-7 Mo or 17-7PH stainless steels referred to above which in a ductile (annealed) condition allows portions of the turns along one side of the coil to be compressed, in turn causing the material of the coil to form a projection which engages the next successive turn of the coil. The projections so formed may simply contact the next portion of the coil in which case the internal wire may only be used as a tension or pull wire, the individual projections extending from turns of the coil serving only to prevent relative movement of the individual turns of the coil toward one another. However, the tabs or projections so formed may alternatively be welded to the next successive coil member, also preventing relative movement of individual ones of the coils apart from one another, along the side of the coil in which the tabs or projections are formed. In this embodiment, it is preferable that the tabs or projections are formed such that their base width is greater than the arc height of the section of the coil across which the tabs extend, in order to provide increased resistance to out of plane twisting of the coil during longitudinal movement of the internal wire.
In all embodiments in which wrought stainless steels as discussed above or similar materials are employed for the coil and backbone, the coil and backbone are preferably fabricated from the metal in its annealed, relatively softer ductile condition, allowing winding of the coil without substantial spring-back and facilitating any required stamping or forming operations performed on the coil or backbone. The coil and backbone are then preferably welded to one another. Following assembly of the coil and backbone assembly and any welding of the components to one another, the assembly is preferably heat treated and stress relieved to temper the assembly and produce a desired final set of mechanical embodiments, properties (hardness, spring constant, tensile strength, etc.). In some the tubing making up the majority of the stylet body may also be formed of such alloys and welded to the coil and core, preferably prior to heat treatment.